The present invention relates to the electrosynthesis of metal carboxylates. In the conventional thermal batch method of synthesizing metal carboxylates, a fine powder of the metal is suspended in an organic solvent which includes an organic acid. Reaction is effected by heating the mixture at elevated temperatures for a predetermined period of time. In another known method, a halide salt of the metal is dissolved in an aqueous solution containing an alkali metal carboxylate, and the metal carboxylate precipitates out of solution.
Electrosynthesis of metal carboxylates is known, but the use of an emulsion in such a process is not. International application number PCT/GB85/00054, published Aug. 15, 1985 under Publication No. WO 85/03530, discloses the preparation of heavy metal carboxylates through an electrolytic method. The publication states that an electric current is passed through an anode comprising a heavy metal and an inert cathode in an aqueous electrolyte containing at least one carboxylic acid. A heavy metal carboxylate results. The PCT application discloses that the carboxylic acid can be miscible in the aqueous solution, immiscible in the solution, or insoluble in the solution. In the case where the acid is immiscible, the application does not disclose or suggest the use of an emulsion but, rather, indicates that the acid itself can be a liquid layer separate from the aqueous solution.
Unlike the use of a separate layer of an immiscible carboxylic acid, the use of an emulsion, in accord with the present invention, offers several advantages. First, faster reaction times result because an emulsion provides greater surface area for reaction between the metal and the carboxylic acid. Second, a clean product results because of the selective extraction of the metal carboxylate into the organic phase. These two advantages are the unexpected result of the interfacial equilibrium between the organic suspension within the aqueous solution.
The metal carboxylates produced according to the invention described and claimed herein generally can be classified as metallic soaps. Metallic soaps are a group of water insoluble compounds containing alkaline earth or heavy metals combined with monobasic carboxylic acids. Metallic soaps are classified as acid soaps containing free acid (positive acid number), neutral soaps containing no free acid (zero acid number), or basic soaps which are characterized by a higher metal-to-acid equivalent ratio than the stoichiometric amount. Metallic soaps can be used as, among other things, stabilizers for plastics, fungicides, catalysts, driers, and fuel additives. The most important group of the metallic soaps are the "driers" which promote and accelerate the drying, curing, or hardening of oxidizable coating vehicles such as paints.